1. Field of the Invention
The present invention relates to a method and related communications device for managing operation of control channels, and more particularly, to a method and related communications device for managing operation of control channels used in Continuous Packet Connectivity (CPC) for a user end in a wireless communications system.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting at the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate. For HSDPA and HSUPA, the 3rd Generation Partnership Project (3GPP) provides a Continuous Packet Connectivity (CPC) protocol specification, which includes features that, for user equipments (UEs) in CELL_DCH state, aim to significantly increase the number of packet data users for a cell, reduce the uplink noise rise and improve the achievable download capacity for VoIP.
For an HSDPA UE, physical channels include a high speed physical downlink shared channel (HS-PDSCH), for transferring payload data, and a high speed physical control channel (HS-DPCCH) for uploading an acknowledgement/negative acknowledgement (ACK/NACK) and a channel quality identifier (CQI). As for the media access control (MAC) layer of the HSDPA UE, a MAC-hs entity utilizes a transport channel of High Speed Downlink Shared Channel (HS-DSCH) for receiving data from the physical layer. In addition, a shared control channel for HS-DSCH (HS-SCCH) is used as a physical downlink channel, responsible for transmission of control signals corresponding to HS-DSCH, such as demodulation information.
For an HSUPA UE, physical channels includes two uplink transport channels: an E-DCH dedicated physical data channel (E-DPDCH), for transferring payload data, and an E-DCH dedicated physical control channel (E-DPCCH) for transmission of control signals, such as retransmission numbers. Furthermore, a bundle of downlink physical channels are employed in the HSUPA system and used for transmitting control signals associated with grants, ACKs and etc. The downlink physical channels include E-DCH relative grant channel (E-RGCH), E-DCH absolute grant channel (E-AGCH), E-DCH HARQ acknowledgement indicator channel (E-HICH) and fractional dedicated physical channel (F-DPCH). As for the MAC layer of the HSUPA UE, a MAC-e/es entity utilizes a transport channel of Enhanced Dedicated Transport Channel (E-DCH) for transmitting MAC packet data to the physical layer with supporting a transmission time interval (TTI) of 10 milliseconds (ms) or 2 ms.
CPC includes an HS-SCCH less operation, which is a special mode of HSDPA operation for reducing HS-SCCH overhead for a hybrid automatic repeat request (HARQ) process, thereby reducing UE power consumption. Under this mode, the first HS-DSCH transmission of the HARQ process corresponding to small transport blocks (TBs) on pre-defined HS-DSCH is performed without accompaniment of HS-SCCH signaling, and the HARQ retransmissions corresponding to the first HS-DSCH transmission are accompanied with the HS-SCCH signaling if the retransmissions are needed. Accordingly, the UE needs blind decoding for TB data of the first transmission based on predefined TB size and channel coding set. If blind decoding is success, the UE reports ACK to the base station, also known Node-B, through HS-SCCH; otherwise, the UE reports nothing and waits for retransmission initiated by the Node-B. In order to combine the first transmission with the subsequent retransmissions, the HS-SCCH transmits required control signals of physical channel coding set, TB size, UE identity, a pointer and etc., where the pointer notify the UE of the TTI where the previous transmission has been performed. In addition, The UE can report ACK or NACK for the retransmission, and the retransmission is restricted to two times. The first and second retransmissions can be asynchronous with respect to the first transmission, and with respect to each other. The accompanying HS-SCCH follows the same timing relationship with the HS-PDSCH transmission as legacy transmissions do.
As to radio resource control (RRC), the UE and the network, such as the Node-B or a radio network controller (RNC), can configure the CPC by exchanging RRC messages and information elements (IEs) that include corresponding parameters. According to the RRC protocol specification of 3GPP, a Continuous Packet Connectivity HS-SCCH Less Information IE is provided to carry the configuration of “HS-PDSCH Code Index”, “Transport Block Size Index” and etc. In general, the above IE can be included in RRC CONNECTION SETUP, ACTIVE SET UPDATE, CELL UPDATE CONFIRM or other reconfiguration messages, and can be transmitted to the UE through RRC procedures. On the other hand, the UE stores the configuration includes in the reconfiguration messages into a CPC_HS_SCCH_LESS_PARAMS variable.
Furthermore, the UE includes a CPC_HS_SCCH_LESS_STATUS variable having two possible values of “TRUE” and “FALSE, which represent the in-use state and the out-of-use state of the HS-SCCH less operation, respectively. According to the RRC specification, the UE is required to determine the value for CPC_HS_SCCH_LESS_STATUS variable if receiving any reconfiguration messages. Within the CPC_HS_SCCH_LESS_STATUS determination, the CPC_HS_SCCH_LESS_STATUS variable shall be set to “TRUE” when all of the following conditions are met:                1. the UE is in CELL_DCH state;        2. an HS_DSCH RECEPTION variable is set to “TRUE”;        3. no DCH transport channel is configured;        4. the CPC_HS_SCCH_LESS_PARAMS is set;        5. the UE has received a Continuous Packet Connectivity HS-SCCH Less information IE from the latest reconfiguration message.        
If any of the above conditions is not met and the CPC_HS_SCCH_LESS_STATUS variable is set to be “TRUE”, the UE shall:
1. set the CPC_HS_SCCH_LESS_STATUS variable to be “FALSE”;
2. clear the CPC_HS_SCCH_LESS_PARAMS variable;
3. stop all related activities of CPC HS-SCCH less operation.
Whenever the CPC_HS_SCCH_LESS_STATUS variable is set to “TRUE”, the UE shall configure the physical and MAC layers to operate according to the CPC_HS_SCCH_LESS_PARAMS.
According to the above, the UE determines the value for CPC_HS_SCCH_LESS_STATUS variable only when receiving reconfiguration messages, and the HS-SCCH less operation is only applied to the UE in CELL_DCH. If a radio link failure or a radio link control (RLC) unrecoverable error occurs or if transmission of a UE CAPABILITY INFORMATION message fails during HS-SCCH less operation, the UE shall perform a cell update procedure to remedy those situations. When initiating the cell update procedure, the UE shall move to CELL_FACH state and select a suitable UMTS radio access (UTRA) cell for submitting a CELL UPDATE message. However, the prior art specification specifies no related actions of HS-SCCH less operation under the abovementioned situations. As a result, the UE of the prior art does not re-determine the CPC_HS_SCCH_LESS_STATUS variable when moving out of CELL_DCH state. That is, the UE continues applying HS-SCCH less operation in CELL_FACH state, which is not applicable for HS-SCCH less operation. This may cause severe errors in the physical and MAC layers of the UE.
The radio link failure may occur when the UE is situated in poor signal distributing area, such as a basement or rural area with small coverage. The RLC unrecoverable error is likely to occur due to many causes, such as RLC reset errors or RLC recovery errors. The UE CAPABILITY INFORMATION message is utilized to notify the UTRAN of information of specific UE capability (ex. radio access capability).